If you join without felting, won’t it slip out since it’s so thin and loose with the kitting?
I think this is what you’re looking for. Scroll down to “Joining Non-Wool Yarns For Lace.” It’s a very clever technique that I haven’t seen anywhere else. I’ve used it with non-feltable chunky yarn with good results, so it can be used for projects other than lace. 
That looks brilliant! Thank you so much! 